The softswitches that route VOIP calls get caller ID info off the PSTN (public switched telephone network), but they dont play by the PSTNs FCC-mandated rules. Those rules and switching protocols make regulated telcos validate that caller ID and block it if requested. They dont apply (yet) to VOIP. Which is why, if you get a call from an IP phone network, you cant trust the caller ID; it may be spoofed. Worse, you cant trust your own caller ID to be blocked if youre calling an IP phone.
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